Magnetic material



Patented Apr. 18,1939

Cross Reference PATENT OFFICE MAGNETIC MATERIAL Irvin W. Cox, Chicago, Ill.-, assignor to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware No Drawing. Application December 30, 1935,

Serial No. 56,725

5 Claims.

My invention relates in general to magnetic material and more specifically to an improved magnetic material for use in loading coils for telephone circuits or for use in impedance or inductance coils, and the method of producing the material and forming it into useful structures.

The main object is to produce a material having low core losses and a relatively high permeability in order to provide a highly efficient coil with a core of the smallest possible size. In order to accomplish this object it is customary to use a powdered or finely divided magnetic dust and it is necessary to, as nearly as possible, completely insulate the individual grains of the magnetic dust and provide an efilcient binder to hold the dust together in as close relation as possible without rupturing the insulating envelope.

In accordance with the present embodiment the present invention contemplates the construction of magnetic cores of powdered iron particles insulated and pressed into cores in the manner hefi naiter specified although metal particles of nickel-iron 9r any other alloy may of course be use esire e me a mixed with colloidal andalusite in dry form, then mixed'with er suc as sodium silicate in a solution. Heat is applied du'r ng ast xing untilthe binder has dried. An gxidizersuch as ammonium chromatmen added to the particles for the purpose of oxidizing any of the facets of the particles which may have been left uncoated by the andalusite in the binder and they are then pressed into cores. The cores are then heat treated to a temperature suillcient to liberate oxygen from the oxidizer to oxidize the uncoated facets of metal and the cores are ready' for winding.

Following is a more detailed description of the method employed in treating the i r;gn particles. As stated, I prefer to use a powdered iron or iron dust of sufilcient fineness to pass through a screen of 300 mesh. The dust may be powdered in any of the well known methods. The iron particles are first mixed with about .5% by weight of co lloi dal andalusite, the two being thoroughly mixed together by tumbling dry for about twenty minutes. -Andalusite is an anhydrous insoluble mineral found in nature and is the preferred insulator due to-there being no change in volume due to loss of water of crystallization during heat treatment. Another material which may be used i f desired is anextremely finely divided asbestos fibre. After mixing the iron with the mm anaalusite an alkaline solution of sodium silicate is prepared and the iron is mixa with about particles are first 2.6% by weight of the solution. This mixture is then tumbled to dryness and then subjected to a temperature of approximately ISOLQQQtigradeto bake the binder so as to homhfiii'swafor" in 'place.

As previously stated, there may be certain surfaces or facets of the iron particles which are not completely covered or coated by the insulator and in order to insure insulation of these facets I now add about .3% bvweight of an 251mm; such as ammoniw ghromate to the mixture. Other su s ances such as aluminum chlorate or sodium chlorate may be used and these materials are chosen due to their stability at mixing temperatures and to the fact that oxygen is released at slightly higher temperatures for oxidizing the uninsulated facets of the particles. The reason for choosing an oxidizer of this type is that during pressing it is possible that certain 10! the insulating envelopes around the particles may be pierced or punctured and it is very desirable to have an oxidizer which will not release its oxygen during mixing or pressing but only when heated to a higher temperature after pressing. The oxygen when released can follow the grain boundaries to more completely insulate each grain by oxidation at a time when no further working of the material will occur. Because ammonium eliminate-completely releases its oxygen content at a very definite temperature, it has the qualities which make it the preferred oxidizer for this use. In other words, it not only releases its oxygen at a definite temperature, but completely releases its whole content so as to insure that no further oxidation will occur later. This insures theproduction of a core which will remain stable over a period of years. The mixture of the insulated iron and the oxidizer is now again tumbled to dryness and the temperature brought to 105 tolllilf centigrade in about an hour to complete drying.

' The material is now ready for pressing into cores and they are so formed by pressih'g'the ma-.

EXAMINER What I consider to be novel is set forth in the following claims.

What is claimed is:

1. The method of making magnetic structures which consists in first coating particles of a magnetic material with an insulating material, then adding to the insulated material a substance which liberates oxygen when heated to 160 0.. then pressing the insulated material into cores. and heating the cores above 150 C. to cause oxy-' gen to be liberated in said substance to oxidize any uninsulated portions of the material.

2. The method of making magnetic structures which consists in first mixing magnetic material with colloidal andalusite, adding a solution of sodium silicate as a binder, drying the mixture and then adding a solution of ammonium chromate as an oxidizer, then pressing the material into cores, and then heating the cores to a temperature sufflcient to cause the oxidizer to liberate oxygen to oxidize any exposed uninsulated surfaces of the magneticmaterial.

3. The method of producing magnetic structures which consists in coating the particles of magnetic material with sodium silicate binder andcolloidal andalusite, in heating the insulated particles to dryness, in adding a solution of ammonium chromate and heating to dryness, pressing the material into cores, then heating the pressed cores to a sufllcient temperature to cause the decomposition of the ammonium chromate and consequent liberation of oxygen, to cause oxidation of any uninsulated surfaces of the magnetic particles. A

51. The method of insulating powdered iron particles which consists in first mixing the particles with colloidal andalusite, then adding a solution of sodium silicate to the mixture and drying. then adding a solution of ammonium chromate to the mixture and drying, then pressing the treated material into cores and thereafter heating the cores to a temperature sun'icient to decompose 

